Systems and methods for two-step self-servowriting using per-head final pattern writing

ABSTRACT

A two-step self-servowriting process first writes an intermediate pattern based on a reference pattern, and then writes a final pattern based on the intermediate pattern, wherein the reference pattern can be a printed media pattern. Such an approach can be utilized to reduce the noise/runout, eliminate timing eccentricity, and increase the sample rate of the final pattern. In addition, a disk drive containing multiple rotatable disks can perform two-step self servowriting using either a per-head self-servowriting process to further improve written-in runout. In such a process, intermediate servo patterns can be written via each head in the drive, and the final servo patterns can be written and/or re-written via each head either individually. This description is not intended to be a complete description of, or limit the scope of, the invention. Other features, aspects, and objects of the invention can be obtained from a review of the specification, the figures, and the claims.

CLAIM OF PRIORITY

This application claims priority from the following application, whichis hereby incorporated by reference in its entirety:

U.S. Provisional patent application No. 60/586,195, entitled SYSTEMS ANDMETHODS FOR TWO-STEP SELF SERVOWRITING, by Richard M. Ehrlich et al,filed Jul. 8, 2004.

INCORPORATION BY REFERENCE

This application is related to the following patent which is herebyincorporated by reference in its entirety:

U.S. Pat. No. 6,738,205, SELF-WRITING OF SERVO PATTERNS IN DISK DRIVES,Inventors: Patrick Moran et al., filed on Jul. 8, 2001.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following co-pending applicationwhich is hereby incorporated by reference in its entirety:

U.S. patent application Ser. No. 11/003,605, entitled SYSTEMS ANDMETHODS FOR TWO-STEP SELF-SERVOWRITING USING OPTIMAL INTERMEDIATEPATTERN by Richatd M. Ehrlich, filed concurrently.

FIELD OF THE INVENTION

The present invention relates to the writing of position information torotatable media.

BACKGROUND

Advances in data storage technology have provided for ever-increasingstorage capability in devices such as DVD-ROMs, optical drives, and diskdrives. In hard disk drives, for example, the width of a written datatrack has decreased due in part to advances in read/write headtechnology, as well as in reading, writing, and positioningtechnologies. More narrow data tracks result in higher density drives,which is good for the consumer but creates new challenges for drivemanufacturers. As the density of the data increases, the tolerance forerror in the position of a drive component such as a read/write headdecreases. As the position of such a head relative to a data trackbecomes more important, so too does the placement of information, suchas servo data, that is used to determine the position of a head relativeto a data track.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing components of an exemplary drive system thatcan be used in accordance with various embodiments of the presentinvention.

FIG. 2 is a diagram showing an example of a data and servo format for adisk in the drive of FIG. 1.

FIG. 3 is a diagram showing servo information that can be written to thetracks shown in FIG. 2.

FIGS. 4( a)–(f) are diagrams of a servo-burst pattern being written overa progression of servowriting steps.

FIG. 5 is a diagram of a disk stack containing a printed referencepattern that can be used with the system of FIG. 1.

FIG. 6 is a diagram showing various views of portion of a magneticpattern that can be used with the system of FIG. 1.

FIG. 7 is a diagram showing a phase burst and corresponding read signalsthat can be used with the system of FIG. 1.

FIG. 8 is a plot showing an exemplary sampling approach that can be usedwith the signals of FIG. 6 and FIG. 7.

FIG. 9 is a diagram showing relative burst phases that can be used withthe system of FIG. 1.

FIG. 10 is a diagram showing a reference pattern in a disk stack thatcan be used in the system of FIG. 1.

FIG. 11 is a diagram showing a printed reference pattern andintermediate pattern that can be used with the system of FIG. 1.

FIG. 12 is a flowchart showing a process that can be used with thesystem of FIG. 1.

FIG. 13 is a flowchart showing a process that can be used with thesystem of FIG. 1.

FIG. 14 is a flowchart showing a process that can be used with thesystem of FIG. 1.

FIG. 15 is a flowchart showing a process that can be used with thesystem of FIG. 1.

FIG. 16 is a flowchart showing a process that can be used with thesystem of FIG. 1.

DETAILED DESCRIPTION

Systems and methods in accordance with various embodiments of thepresent invention can be used when servowriting, or self-servowriting, arotatable storage medium in a data storage device, such as a hard diskdrive. For example, a typical disk drive 100, as shown in FIG. 1,includes at least one magnetic disk 102 capable of storing informationon at least one of the surfaces of the disk(s). A closed-loop servosystem can be used to move an actuator arm 106 and data head 104 overthe surface of the disk(s), such that information can be written to, andread from, the surface of the disk(s). The closed-loop servo system cancontain, for example, a voice coil motor driver 108 to drive currentthrough a voice coil motor (not shown) in order to drive the actuatorarm, a spindle motor driver 112 to drive current through a spindle motor(not shown) in order to rotate the disk(s), a microprocessor 120 tocontrol the motors, and a disk controller 118 to transfer informationbetween the microprocessor, buffer memory 110, read channel 114, and ahost 122. A host can be any device, apparatus, or system capable ofutilizing the data storage device, such as a personal computer or Webserver or consumer electronics device. The drive can contain at leastone processor, or microprocessor 120, that can process information forthe disk controller 118, read/write channel 114, VCM driver 108, orspindle driver 112. The microprocessor can also include a servocontroller, which can exist as an algorithm resident in themicroprocessor 120. The disk controller 118, which can store informationin buffer memory 110 resident in the drive, can also provide user datato a read/write channel 114, which can send data signals to a currentamplifier or preamp 116 to be written to the disk(s) 102, and can sendservo and/or user data signals back to the disk controller 118.

The information stored on such disk(s) can be written in concentrictracks, extending from near the inner diameter to near the outerdiameter of the disk 200, as shown in the example disk of FIG. 2. In anembedded servo-type system, servo information can be written in servowedges 202, and can be recorded on tracks 204 that can also containdata. In a system where the actuator arm rotates about a pivot pointsuch as a bearing, the servo wedges may not extend linearly from theinner diameter (ID) of the disk(s) to the outer diameter (OD), but maybe curved slightly in order to adjust for the trajectory of the head asit sweeps across the disk(s).

The servo information often includes bursts of transitions called “servobursts.” The servo information can be positioned regularly about eachtrack, such that when a data head reads the servo information, arelative position of the head can be determined that can be used by aservo processor to adjust the position of the head relative to thetrack. For each servo wedge, this relative position can be determined inone example as a function of the target location, a track number readfrom the servo wedge, and the amplitudes or phases of the bursts, or asubset of those bursts. A measure of the position of a head or element,such as a read/write head or element, relative to the center of a targettrack, will be referred to herein as a position-error signal (PES).

For example, a centerline 300 for a given data track can be “defined”relative to a series of bursts, burst edges, or burst boundaries, suchas a burst boundary defined by the lower edge of A-burst 302 and theupper edge of B-burst 304 in FIG. 3. The centerline can also be definedby, or offset relative to, any function or combination of bursts orburst patterns. As a non-limiting example, a centerline defined by fourbursts can be referred to as “4-burst-centerline” as described forexample, in U.S. Pat. No. 5,381,281 entitled “Disk Drive System UsingMultiple Embedded Quadrature Servo Fields”, by Louis J. Shrinkle, et al,filed Jun. 24, 1993. The definition of a track centerline can include,for example, a location at which the PES value is a maximum, a minimum,or a fraction or percentage thereof. Any location relative to a functionof the bursts can be selected to define track position. For example, ifa read head evenly straddles an A-burst and a B-burst, or portionsthereof, then servo demodulation circuitry in communication with thehead can produce equal amplitude measurements for the two bursts, as theportion of the signal coming from the A-burst above the centerline isapproximately equal in amplitude to the portion coming from the B-burstbelow the centerline. The resulting computed PES can be zero if theradial location defined by the A-burst/B-burst (A/B) combination, or A/Bboundary, is the center of a data track, or a track centerline. In suchan embodiment, the radial location at which the PES value is zero can bereferred to as a null-point. Null-points can be used in each servo wedgeto define a relative position of a track. If the head is too far towardsthe outer diameter of the disk(s), or above the centerline in FIG. 3,then there will be a greater contribution from the A-burst that resultsin a more “negative” PES. Using the negative PES, the servo controllercould direct the voice coil motor to move the head toward the innerdiameter of the disk(s) and closer to its desired position relative tothe centerline. This can be done for each set of burst edges definingthe shape of that track about the disk(s).

The PES scheme described above is one of many possible schemes forcombining the track number read from a servo wedge and the phases oramplitudes of the servo bursts. Many other schemes are possible that canbenefit from embodiments in accordance with the present invention

A problem that exists in the reading and writing of servo informationsuch as servo patterns involves the misplacement, or offset, of aread/write head with respect to the ideal and/or actual position of atrack. It is impossible to perfectly position a head with respect to atrack for each rotation of disk(s), as there is almost always anoticeable offset between the desired position and the actual positionof the head with respect to the disk(s). This can cause problems whenwriting servo patterns, as each portion of the pattern can be slightlymisplaced. This can lead to what is referred to as “written-in runout.”Written-in runout can be thought of as the offset between the actualcenterline, or desired radial center, of a track and the centerline thatwould be determined by a head reading the written servo pattern.Written-in runout can lead to servo performance problems, wasted spaceon disk(s) and, in a worst case, unrecoverable or irreparably damageddata.

Additional servowriting steps can be used when writing servoinformation. The use of additional servowriting steps for the writingand/or trimming of servo burst patterns, for example, can provide for alow written-in runout in a servo pattern, but at the cost of sometime-penalties in the servowriting and/or self-servowriting operations.For the discussion in this application, a “servowriting step” involveseither:

-   a) writing digital information, writing one complete burst, and    trimming another, or-   b) writing one complete burst, and trimming another.    And a “pass” commonly used in the industry involves one or more of:-   a) writing digital information and a burst;-   b) writing just a burst;-   c) writing digital information and trimming a burst; and-   d) trimming a burst.    For either a step or a pass, an action occurs for all wedges around    the disk. In contrast, a “revolution” involves doing at least one of    the actions involved in a pass, but possibly only for a subset of    all the wedges around the disk.

FIGS. 4( a)–4(f) depict the progression of several servowriting steps ofan exemplary servowriting process. The pattern shown in these figures iscommonly referred to in the industry as a 3-pass-per-track,trimmed-burst pattern, for reasons described below. Using thenomenclature of this document, one could refer to the pattern as a“3-servowriting-step-per-track, trimmed-burst” pattern. Each figuredepicts a small portion of the surface of disk(s). This portion cancontain several servo tracks, extending radially on the disk(s) andvertically in the figures, and can cover the space of a single servowedge, circumferentially on the disk(s) and horizontally in the figures.A typical drive can have tens of thousands of servo tracks, and over onehundred wedges per revolution. In the figures, the black areas indicateportions of the surface of the disk(s) that have been magnetized in onedirection. The white areas have been magnetized in another direction,typically in a direction opposite to that of the patterned areas. For adrive that uses longitudinal recording, the two directions can be in thepositive and negative circumferential directions. For a drive that usesvertical recording technology (also sometimes referred to in theindustry as “perpendicular recording”), the two directions can beperpendicular to the recording surface, such as would be “in” and “out”of the page for the illustrations of FIGS. 4( a)–(f). These simplifiedfigures do not show effects of side writing of the write element, whichcan produce non-longitudinal magnetization and erase bands. Such effectsare not of primary importance to the discussion herein.

In FIG. 4( a), the result of a single servowriting step is shown. Fromthat step, the servowriting head (passing from left to right in thefigure) has written an exemplary servo pattern containing a preamble,followed by a servo-address mark (SAM), followed by an INDEX-bit, andthen a track number, as is known in the art. Other information can bewritten to the servo pattern in addition to, or in place of, theinformation shown in FIG. 4( a). An INDEX-bit, for example, is one pieceof information that can be used to give the servo an indication of whichwedge is wedge-number zero, useful for determining circumferentialposition. The track number, which can be a graycoded track-number, canlater be used by the servo to determine the coarse radial position ofthe read/write (R/W) head (note that the bits representing the tracknumber shown here are for illustration purpose only, a typical drive mayhave up to 18 or more track number bits). Following the track number,the head writes one of four servo bursts, in this case what will bereferred to as a C-burst, which can later be used by a servo todetermine the fine (fractional track) radial position of a R/W head. Thenumber of servo bursts used can vary with servo pattern. The burst thatis written can be, for example, the one that is in-line with the digitalinformation. The width of the written track can be determined by themagnetic write-width of the write element of the servowriting head.

FIG. 4( b) shows the result of a second servowriting step of theservowriting head. All that has been added in the second step is anadditional burst, in this case referred to as an A-burst. The A-burst isdisplaced longitudinally from both the digital information and theC-burst, to prevent any overlap in the longitudinal direction. TheA-burst is also displaced by approximately one-half of a servo-track inthe radial direction.

FIG. 4( c) shows the magnetization pattern after three servowritingsteps of the servowriting head. The new portion of the pattern has beenwritten with the servowriting head displaced another half servo trackradially, for a total displacement of one servo-track, or two-thirds ofa data-track, from the position of the head during the firstservowriting step. New digital information has been written, includingthe same preamble, SAM, and INDEX-bit, as well as a new track number. AD-burst was added during the third servowriting step, and the C-burstwas “trimmed.” The C-burst was trimmed by “erasing” the portion of theC-burst under the servowriting head as the head passed over the burst onthe third servowriting step. As long as the servowriting head is atleast two-thirds of a data-track in radial extent, the digitalinformation will extend across the entire radial extent of theservo-written pattern. This trimming of the C-burst and writing of theD-burst created a common edge position or “boundary” between the twobursts.

In FIG. 4( d), a B-burst has been added and the A-burst trimmed in thefourth servowriting step of the servowriter. At a point in time afterthe servowriting is complete, such as during normal operation of thedisk drive, the upper edge of the B-burst and the lower edge of theA-burst can be used by the servo, along with the graycoded track-numberwhose radial center is aligned with the burst edges, to determine theR/W head position when it is in the vicinity of the center of that servotrack. If a reader evenly straddles the A-burst and the B-burst, theamplitude of the signals from the two bursts will be approximately equaland the fractional Position-Error Signal (PES) derived from those burstswill be about 0. If the reader is off-center, the PES will be non-zero,indicating that the amplitude read from the A-burst is either greaterthan or less than the amplitude read from the B-burst, as indicated bythe polarity of the PES signal. The position of the head can then beadjusted accordingly. For instance, a negative PES might indicate thatthe amplitude read from the A-burst is greater than the amplitude readfrom the B-burst. In this case, the head is too far above the centerposition (using the portion of the pattern in the figure) and should bemoved radially downward/inward until the PES signal is approximately 0.It should be noted that for other portions of the pattern a B-burstcould be above an A-burst, resulting in a smaller amplitude contributioncoming from the A-burst when the head is too near the outer diameter ofthe disk(s).

FIGS. 4( e) and 4(f) show the results of subsequent steps of theservowriting process, which has produced a number of servo tracks. Afterthe first step in this process, each subsequent step writes one servoburst in a wedge and trims another. Every second step also writesdigital information, including the SAM and track number. Betweenservowriting steps, the servowriting head is stepped by one-half servotrack radially, either toward the inner diameter (ID) or outer diameter(OD) of the disk(s), depending on the radial direction used to write theservo information. A seek typically takes anywhere from one quarter toone half of the time it takes for the disk(s) to make one revolution.The process of writing the servo pattern for each step typically takesone or two full revolutions to write all of the wedges in that pass. Itis possible that completing the burst writing and trimming for a singleservowriting step can take more than two revolutions, but a maximum oftwo revolutions (one to write the new burst, and another to trim apreviously-written burst) will be considered for the discussion below.

Using such an algorithm, servowriting can take about 1.25–2.5revolutions per servowriting step. Since there are two servowritingsteps per servo-track in this example, and 1.5 servo tracks perdata-track, such a process requires 3 servowriting steps per data-track,or 3.75–7.5 revolutions per data-track. For purposes of subsequentdiscussion only, it will be assumed that the process takes 4 revolutionsper data-track (a relatively low bound).

A disk drive can have tens of thousands of data tracks. With 100,000data-tracks and a spin-speed of 5400 RPM (90 Hz), for example, theprocess would take 4,444 seconds, or about 75 minutes. If the process iscarried out on an expensive servowriter, this can add substantially tothe cost of the drive. Thus, drive manufacturers are motivated to useself-servowriting techniques to reduce or eliminate the time that adrive must spend on a servowriter.

One such technique uses a media-writer to write servo patterns on astack of disks. Each disk is then placed in a separate drive containingmultiple blank disks, such that the drive can use the patterned disk asa reference to re-write servo patterns on all of the other disk surfacesin the drive. The media-writer can be an expensive instrument, and itmay still take a very long time to write a reference pattern on thestack of disks. However, if a stack contains 10 blank disks, forexample, then the media-writer can write the reference pattern for 10drives in the time that it would have taken to servowrite a singledrive. This scheme is a member of a class of self-servowritingtechniques commonly known as “replication” self-servowriting. A typicalreplication process, in which a drive servos on the reference patternand writes final servo patterns on all surfaces, can take place whilethe drive is in a relatively inexpensive test-rack, connected to only apower-supply. The extra time that it takes is therefore usuallyacceptable.

Another class of self-servowriting techniques is known as “propagation”self-servowriting. Schemes in this class differ from those in the“replication” class in the fact that the wedges written by the drive atone point in the process are later used as reference wedges for othertracks. These schemes are thus “self-propagating”. Typically, suchschemes require a R/W head that has a large radial offset between theread and write elements, so that the drive can servo with the readelement over previously-written servo wedges while the write element iswriting new servo wedges. In one such application, a servowriter is usedfor a short time to write a small “guide” pattern on a disk that isalready assembled in a drive. The drive then propagates the patternacross the disk (as described for example, in U.S. Pat. No. 6,631,046entitled “Servo Track Writing Using Extended Copying with Head Offset”).In this type of self-servowriting operation, previously written trackscan later serve as reference tracks.

Many self-servowriting techniques require considerably more than fourdisk revolutions per data-track written, as the drive must spendconsiderable time before each servowriting step determining thewritten-in runout of the corresponding reference track, so that theservowriting head can be prevented from following that runout whilewriting the final servo pattern. Techniques exist which allow tracks ofservo information to be made substantially circular, despite the factthat the reference information is not perfectly circular. Theinformation used to remove written-in runout from the track can becalculated in one approach by examining a number of parameters over anumber of revolutions. These parameters can include wedge offsetreduction field (WORF) data values calculated by examining the measuredPES over a number of revolutions of a track, as well as the servo loopcharacteristics. Some possible approaches to calculate WORF are outlinedin U.S. Pat. Nos. 5,793,559 and 6,061,200. A measurement can be made tocharacterize servo loop characteristics, which can be combined with theobserved PES in order to determine the written-in runout of thereference track. Because the servo typically suffers both synchronousand non-synchronous runout (sometimes referred to in the industry as“repeatable” runout (RRO) and “non-repeatable” runout (NRRO),respectively), any measurement intended to determine the synchronousrunout can be affected by the non-synchronous runout. If manyrevolutions of PES data are observed and combined (one possible approachto combine is to synchronously average the PES data, another possibleapproach is outlined in U.S. Pat. Nos. 6,069,764, 6,437,936, 6,563,663and 6,449,116), the effects of the non-synchronous runout can lessen,leaving substantially only synchronous runout. Observing manyrevolutions of PES data, however, can add significantly to the timerequired for determination of the written-in runout. Process engineersmay need to balance the cost and benefit of additional revolutions ofPES data collection in determination of WORF values.

The computed written-in runout values for each servo wedge can bewritten into the servo wedges themselves for later use by the servo, orcan be kept in drive controller memory for immediate use. During aself-servowriting operation, the drive may use the latter option bymeasuring the written-in runout on a reference track and applying it tothe servo by the use of a table in controller memory. Additionalrevolutions of PES measurements for the reference track can be used toreduce the effects of non-synchronous runout.

It has been observed that the written-in runout of amagnetically-printed media reference surface has a relatively highcorrelation from track to track and such correlation gradually decreasesover longer radial distances. It is possible to take advantage of thislocal correlation in written-in runout by using, as a starting-point forone track, the WORF values that have been determined for themost-recently-servowritten track. Under this approach, the current trackfollowed by the reference head while observing its PES values todetermine its WORF-values is already very nearly circular and itsobserved residual PES can be used to determine an incremental change tobe applied to the previously-determined WORF values.

It has also been observed that determining the low-frequency componentsof WORF values can be difficult, due mainly to the very high servoloop-gain of the system at low frequencies. In particular, the so called“1× WORF component” (or the component of the WORF values that variessinusoidally at the spin-speed of the disk) can vary significantly frommeasurement to measurement, as small variations in the 1× component ofmeasured PES may cause relatively large changes in the 1× component ofthe computed WORF values. If the determined 1× components of WORF fortwo adjacent tracks are significantly in error, portions of the twotracks can be “squeezed”, i.e., portions of the two tracks may be closertogether than desired while other portions will be too far apart (andtherefore likely to be too close to their other neighbors). If alltracks of a drive have the same error in the 1× component of their WORFvalues, there would be an un-wanted eccentricity in the entire band ofservowritten tracks, but no added track-squeeze since adjacent trackswould have similar eccentricity. Thus, one solution would be todetermine the 1× component of the WORF values at one track at thebeginning of the servowriting operation, and from that point on, onlyupdate higher-order components of the WORF-values (2×, 3×, 4×, etc.) asthe operation proceeds from step to step. Another solution would be tohave different iterative WORF update-gain for different frequencies. Ifa very low update-gain is used for the 1× WORF harmonic, then variationsin the observed PES value on any one track will not have a large effecton the 1× WORF-values for that track. An extreme case of this strategyis to have zero update-gain for the 1× WORF component, in which case the1× WORF-values used would be the same across the tracks of the drive. Itis possible that one of the above approaches might be appropriate formore than just the 1× WORF component if the servo loop-gain at 2× oreven 3× the spin-speed is also very high.

As previously described, techniques for determining and removingwritten-in runout of a track will hereinafter be referred to as WORFtechnology. If, for example, a drive spends 5 revolutions to determinethe written-in runout of each reference track before writing thecorresponding final wedges, that would add 15 revolutions to the writingtime of each data-track (5 extra revolutions per servowriting step,times 3 servowriting steps per data-track), bringing the total time perdata-track to 19 revolutions.

Even though the self-servowriting time may be as much as about fivetimes as long as the time necessary to servowrite a drive on aservowriter (19 revolutions/data-track, versus 4revolutions/data-track), self-servowriting is likely to be a lessexpensive alternative due to the expense of servowriters, as well as thefact that servowriting operations on a servowriter generally must beperformed in a clean-room environment. Also, as track-densities gethigher it becomes more difficult for an external device such as anactuator push-pin to control the position of the RJW heads accuratelyenough to produce a servo pattern with sufficiently small written-inrunout. The expense of servowriting also rises in proportion to thenumber of tracks on a drive.

In various embodiments of the present invention, the reference patterncan be, but is not limited to, a printed media servo pattern, or aspiral pattern. The spiral pattern is discussed in details in U.S. Pat.No. 5,668,679 entitled “System for Self-Servowriting a Disk Drive”, byPaul A Swearingen, et al, filed Dec. 21, 1995. The printed media servopattern will be utilized to illustrate the present invention in thefollowing discussions.

In a drive system that can be used in accordance with embodiments of thepresent invention, a surface of a magnetic disk 500 can contain aprinted magnetic pattern 502. That magnetic disk can be placed in adrive that may contain other magnetic disks 504, 506 in a disk stack,such as the example stack shown in FIG. 5. The surface of the disk 500having the printed magnetic pattern 502 can be used as a reference foruse while writing final wedges to all disk surfaces in the drive. Theprinted pattern can be used as a reference for information such astiming information, circumferential position information, and/or radialposition information for the disk. The use of a printed media pattern asa reference pattern can allow for a reasonable reduction in anyrepeatable runout written to the reference pattern by reading theprinted signal pattern, perhaps over a number of revolutions at eachradial location, and calculating the written-in runout. The drive systemcan then adjust the read/write head position to compensate for theperceived PES obtained from the reference surface in order toeffectively remove the written-in runout when replicating the servopattern. In some embodiments the runout may not be completely removed,but may be adjusted or modified to a pre-determined amount and/orpattern. Note however that it is not necessary for the printed surfaceto be at one end or the other of the disk-stack as shown in FIG. 5. Infact, it may be desirable to place the printed surface near to themiddle of the stack in order to minimize the maximum offset between thehead-radius on the reference-surface and that on other surfaces (due to,for example, tilt and other factors). The same applies to FIG. 10discussed later.

FIG. 6 shows an exemplary printed signal pattern that can be used inaccordance with embodiments of the present invention, such as in theexemplary disk stack of FIG. 5. The pattern may include one or moreservo wedges, and FIG. 6 shows a reference signal for servo informationcorresponding to a servo wedge 602 on a disk 600. The signal is shown ina variety of formats. An expanded view 604 of the exemplarymagnetization pattern is shown including information for the wedge 602,followed by a signal 606 that could be generated by reading the patternfor the wedge 602. As shown in the Figure, the printed signal patterncontains a preamble, followed by a servo address mark (SAM), and digitalinformation that may include an index-mark. Following the digitalinformation is a pattern portion referred to as a “zig,” a portionreferred to as a “zag,” and (an optional) timing burst.

FIG. 7 shows a close-up view of an exemplary “zag” phase burst 700. On alocal scale, a read element may pass horizontally (in the Figure) acrossthe burst 700. A read/write channel can read such a burst and returnboth a sine or “real” value 702 and a cosine or “imaginary” value 704.The phase of the burst can then be calculated as:

${Phase} = {\arctan\left( \frac{\sin\;\phi}{\cos\;\phi} \right)}$In the “zag” displayed, the magnetization pattern is slanted relative toboth the radial direction (vertical in the Figure) and thecircumferential direction (horizontal in the Figure). When a readelement passes over the slanted burst, the time at which the elementencounters the transitions in the burst can be used to determine theradial position of the element. For instance, the “higher up” the readelement is in the Figure, or more toward the outer diameter (OD) of thedrive, the later the phase transitions are encountered, or the moredelayed the phase of the signal. The phase determination can besimplified using both a “zig” and a “zag,” or regions with different oropposite slants or phases, such that the relative phase between the twocan be examined, wherein the angles of the zig and zag do not have to beexactly opposite of one another. In this way, absolute phase is not anissue as the drive system can look at the relative phase of the twobursts and can get the radial position for each cycle. If the drive goesthrough multiple cycles, the drive can track the number of cyclesencountered while traversing the disk surface from a knownreference-point, as disclosed in U.S. patent application Ser. No.10/732,638, entitled “Methods for Improving Printed Media Self-servoWriting”, by Richard Ehrlich, filed Dec. 10, 2003.

One process utilizing the zig/zag phase bursts is shown in the diagramof FIG. 12. In such a process, a magnetic pattern is created on a disksurface, such as by printing or servowriting, which contains phasebursts for each track of servo information at step 1200. The phasebursts can include zig and zag bursts, and can be included for each orany wedge in the magnetic pattern. A read element, such as on aread/write head, can be passed over at least a portion of a track ofservo information, such as a portion corresponding to a servo wedge atstep 1202. The relative phase of at least two phase bursts, such as azig and a zag for a wedge along a track, can be examined at step 1204.The radial position of the read element relative to the magnetic patterncan be determined using the relative phase at step 1206. The radialposition can be used to adjust the head position(s) when replicatingthat portion of the pattern, either to the same surface or to any othersurface in a drive or disk stack at step 1208. For instance, if theradial position of a burst for a wedge is too far towards the outerdiameter of the pattern, that burst can be moved toward the innerdiameter of the pattern when replicated. Several passes of the head overthe pattern can be taken to reduce the error in the radial positiondetermination.

Certain processes can be executed initially to determine the runout, asit may be desirable to remove the runout, lessen the amount of runout,or alter the runout to a desired amount. Utilizing WORF calculations isone approach that can be used to determine the amount of runout bytaking into account the servo characteristics and determining how muchrunout was present before the servo tried to remove the runout. Afterthe runout is measured, the amount of runout can be determined andremoved.

When decoding phase bursts, a drive system can use an algorithm thattakes an arc tangent of the real and imaginary parts of a discreetFourier transform (DFT) of the burst signal. Existing channels arecapable of sampling the signal and doing a discreet Fourier transform.One such discreet Fourier transform that can be used is given asfollows:

$F_{k} = {\sum\limits_{n = 0}^{N - 1}{f_{n}{\mathbb{e}}^{{- {j2\pi}}\; k\;{n/N}}}}$In this equation, f_(n) is the sequence in time and F_(k) is the Fouriercomponent in frequency space. This “complex” math can be simplified inat least a few situations. For example, a signal can be examined at onequarter of the sample rate. The signal can also be examined at up to onehalf the sample rate using a Nyquist theorem-based approach. Thesesamples can be taken at any appropriate location or interval, such as ator between signal peaks, etc. If the signal 800 is examined at onequarter the sample rate, as shown in FIG. 8 with an “x” marking eachsample location, the coefficients are either +1, 0, or −1. In this case,the real part of the Fourier transform multiplies the signal by +1, 0,−1, 0, . . . and the imaginary part multiplies the signal by 0, +1, 0,−1 . . . , the imaginary part being offset by one sample from the realpart. Therefore, each sample is adding to, subtracting from, or notaffecting the result. An alternative approach is to use coefficients of+1, −1, −1, and +1 for the real part, and +1, +1, −1, −1 for theimaginary part, which can provide for greater immunity to noise sinceall samples will contribute to the sum. The discreet Fourier transformcan then be reduced to an “adder” with no multiplication. A discreetFourier transform of the signal then can be broken down into real andimaginary parts, which can each be squared and added together. Thesquare root of this sum yields the magnitude of the signal.Alternatively, a ratio of the real and imaginary parts can be taken, andan arctangent of the ratio can yield the phase, such as using the arctanequation given above. Using the phase, the system can determine theradial position.

Note that for the above-described DFT-based burst processing to work, itis most convenient to sample the signal at a rate of four samples percycle. Since the frequency of the printed-media signal is very low, thesignal may actually be sampled much more often than four times per cycleto allow the use of the analog filtering circuitry of the channel (whichis designed to deal with much higher-frequency signals). Additional DSPfiltering may be required to filter the signal so that it can bere-sampled at the 4-times-per-cycle rate as described above.

In some drives, it may be necessary to erase any pre-existing “finalwedges” or any signals in the final-wedge area. Such an erase procedurecan be used, for example, on a “virgin” drive or for a re-scan in aself-scan process. In a virgin drive, or a drive to which no data hasbeen written, it can be desirable to erase the final wedge area toensure that no signal exists on the surface of the disk(s). An erasefinal wedge process can be run on all cylinders in a drive.

After running WORF calculations on a reference track, the measuredposition can be calculated. In one embodiment, as shown in FIG. 9, thephase of the “zig” burst 900 and the phase of the “zag” burst 902 can bemeasured. The difference between the phases can be multiplied by anumber of tracks per cycle to obtain the measured radial position. Forexample, one way to calculate the measured position from the relativephases of the bursts can utilize a formula such as:Measured Position=tracksPerCycle*(φzig−φzag)where φzig and φzag can be a function of the phase for the “zig” and“zag” bursts, respectively, covering both linear and non-linear uses ofthe burst-phase. In some embodiments, φzig (and/or φzag) may also befunctions of the overall radial position. That is, they may vary acrossthe stroke of the drive, according to the parameters of the printedpattern. In other embodiments, φ_(zig) and φ_(zag) may simply beproportional to the phases of their corresponding bursts.

A position error signal (PES) then can be calculated for each wedge. PEScan be a function of the location of a read/write head or elementrelative to a disk surface. Once a write element is at the proper radiallocation, or within acceptable radial boundaries, the final wedges canbe written. Wedges can be written using an approach such as a “stagger”approach or a “concurrent” approach. For example, in one such system apre-amplifier allows concurrent writing to all heads, or some of theheads, in a drive. If the drive system does not contain such apre-amplifier, a final wedge can be written for one head. The drive canthen switch heads and write for another head, or for a group of heads.This “stagger” approach may require the drive system to know, and beable to deal with the fact, that wedges are offset in time for certainheads.

Intermediate Patterns

One limitation of existing printed media self-servowrite approachesresults from the use of optical lithographic processes to create patternmasters. While such processes are generally cost effective, the minimumfeature sizes can be limited. The limitations for such processes arecurrently around the 0.3 micron feature size, which can be much largerthan the space between transitions on a final servo pattern. Therefore,optical lithographic processes are often used to print a singlereference pattern instead of each final pattern. Not only is printing asingle surface cheaper than printing all surfaces in a drive, but usinga reference pattern for self-servowrite avoids the use in final wedgesof a low-frequency pattern that does not make efficient use of the spaceon the disk(s). Low-frequency patterns can be noisy, and servoing on alow-frequency printed reference disk can increase the likelihood ofsynchronous runout. While much of this synchronous runout can be removedusing WORF technology, there can also be non-synchronous runout due todisturbances such as air turbulence and noise on the position signal.PES noise on the position signal of a final wedge pattern can typicallybe a very small fraction of the non-synchronous runout, compared withother sources such as air turbulence spindle runout and otherdisturbances external to the drive.

In a printed media pattern, PES noise can be the dominant source ofnon-synchronous runout, which can be significantly more difficult toremove than synchronous runout, due to the low frequency of the printedmedia pattern. While multiple revolutions of WORF calculations canpermit the determination and subsequent removal of much of thesynchronous runout, the non-synchronous runout can remain. If the PES isnoisy, several revolutions may be necessary to determine the synchronousrunout, as the noise can contaminate the signal. The fact that there canbe a lot of noise on the position error signal is itself a limitation toprinted media self-servowrite. The number of wedges also can be limitedin a printed pattern due to the low-frequency aspect of the pattern.

Systems and methods in accordance with various embodiments of thepresent invention can take care of these and other such problems, at acost of possibly increased test time. In such a system, a printedpattern can be used to write an intermediate servo pattern instead of,or in addition to, a final servo pattern. A drive system can servo onthis intermediate pattern in order to write a final pattern. Such asystem can provide for at least two significant advantages. First, anintermediate pattern can be a higher frequency pattern than a printedreference pattern, which can be quite similar to the final pattern. Infact, the intermediate pattern can be essentially the same as the finalpattern, except that the magnitude of the synchronous runout can begreater, due to for example the amount of non-synchronous runout on theprinted pattern. When servoing on an intermediate pattern, thesynchronous runout can be dealt with using WORF technology. Theintermediate pattern can have significantly less PES noise because theintermediate pattern can have a higher frequency. In fact, it ispossible for the drive, while servoing on the intermediate pattern, tosuffer even lower PES-noise than it does while servoing on the finalpattern. This is because the intermediate pattern could utilize longerbursts than the final pattern does, because a slightly higher use of thedisk-area by the intermediate pattern will not cost any additionaloverhead in the final pattern. Further, magnetically printed signals canhave some quality issues, as the printing process does not necessarilyproduce sharp phase transitions.

FIG. 13 shows one such process. A magnetic servo pattern can be printedto a disk surface at step 1300. The printed pattern can be read, forexample, using the read element of a read/write head at step 1302, suchthat an intermediate magnetic servo pattern can be written to at leastone disk surface at step 1304. The intermediate pattern can be createdusing the printed pattern, but can have a frequency that is similar to afinal pattern. The intermediate pattern can be written to the samesurface as the printed pattern, the other surface of the disk, and/or toany other disk surface in a disk stack, or to more than one surface (oreven to all surfaces) of the stack. The intermediate pattern can be thesame as the printed pattern, essentially the same as the final pattern,or different from both. A respective read element can servo on theintermediate pattern to determine pattern runout for each track of thepattern at step 1306. The intermediate pattern and information aboutrunout can be used to write a final pattern to at least one disksurface, with the head position being adjusted to compensate for, and/orsubstantially remove, the runout at step 1308.

The use of an intermediate pattern can also allow for an increasednumber of wedges in a pattern. For example, a wedge in a printed patterncan occupy a certain amount of physical space on a disk surface.Intermediate wedges can be written that take up significantly lessspace, as they can be written with a higher resolution or at a higherfrequency. If a drive designer is willing to erase, write over, or“destroy” the printed wedges, smaller wedges can be written to thedisk(s) in place of the printed wedges. In one example, such as thatshown in FIG. 11, an intermediate wedge 1106 can be written betweenprinted wedges 1102 when going from a printed pattern 1100 to anintermediate pattern 1104. Each written intermediate wedge can alsooccupy less space than a printed wedge, such as ¼'th to ⅛'th as muchspace. In another example, an intermediate wedge can be written aftereach printed wedge. While servoing on the intermediate wedges, which cantake up considerably less space than the printed wedges, the servo canwrite two final wedges for each intermediate wedge, creating adouble-sample-rate final servo pattern. Not only can the intermediatewedges be smaller, but the wedges can also be considered to be of higherquality in a number of ways. For instance, the PES noise can besignificantly lower in the intermediate wedges. The ability to servo onan intermediate pattern should be substantially similar to the abilityto servo on the final pattern. Therefore, if the final drive is going tohave a certain amount of runout, it should be possible to obtain aboutthat amount of runout (or better) by servoing on the intermediate wedgeswhen writing final wedges.

As discussed above before, self-servowriting processes used to writemagnetic patterns typically fall into one of two categories: replicationor propagation. In replication self-servowriting, a pattern on areference disk is copied to other disk surfaces in a drive. Inpropagation self-servowriting, a drive uses a portion of a patternalready written on a disk surface to copy the pattern to other portionsof the surface, and possibly to other surfaces of the drive. The use oftwo-step printed media self-servowrite can be advantageous primarily forreplication systems.

Using intermediate patterns results in smaller PES noise, which shouldresult in smaller non-synchronous runout during the servoing on theintermediate patterns. In addition, the amount of written-in runout(which can be or the same order of the non-synchronous runout sufferedwhile writing) can be substantially lowered by also utilizing many ofthe techniques described herein, such as by taking additional passes towrite servo bursts, or by varying write current while servowriting. Fortechniques where an accurate PES may be essential, a two-step processcan provide a significant advantage. The use of intermediate wedges,whether for replication or propagation, can allow the amount of runoutwritten into the final pattern to be on the order of or substantiallyless than the amount of non-synchronous runout encountered whileservoing. As long as a drive has acceptable non-synchronous runout inthe final product, it should be possible to self-servowrite. Otherimprovements to servowriting can also be used, such as improvements toreduce air turbulence and disk vibration.

Using an intermediate pattern does not mean that the amount ofservowriting time is necessarily doubled. Such a system can take fewerrevolutions for WORF calculations when writing the intermediate wedges,as reducing the synchronous runout of the intermediate wedges to theabsolute minimum may not be necessary. Intermediate patterns can bewritten that provide the benefits of a higher frequency pattern withoutrequiring as many steps as writing the final pattern. Instead of takingtwice as long, it can take on the order of 50% longer to write anintermediate pattern, or on the order of about 25% longer, dependingupon decisions made regarding the writing of the intermediate pattern.

Other advantages of an intermediate wedge approach can be obtained usingsuch systems. For example, the reduction in PES noise obtained throughuse of an intermediate pattern can allow the use of write currentvariation in self-servowriting. Write current variation is described,for example, in U.S. patent application Ser. No. 10/420,076 entitled“Systems for Self-Servowriting Using Write-Current Variation,” byRichard M. Ehrlich, filed Apr. 22, 2003. Without the use of intermediatepatterns, the PES noise can be too great to properly determine theappropriate write current.

Timing Eccentricity

One important application of the intermediate wedge approach can be toincrease flexibility in elimination of timing eccentricity. A referencepattern can have a substantial frequency variation due to factors suchas a mis-centering of the pattern. As a result, the amount of timebetween printed pattern wedges encountered by a read element can alsovary due to the mis-centering, causing a disk in a drive to exhibit socalled timing eccentricity in addition to radial runout. It can bedesirable to remove any timing eccentricity, as having uniform spacing(and thus equal amount of time) between wedges of a pattern can make iteasier to format the drive.

Under the single-step self-servowriting approach, the final servopattern is written directly using printed pattern without utilizing theintermediate pattern. In order to remove timing eccentricity under suchapproach, ample space should be reserved between the ends ofmis-centered and thus non-uniformly-spaced printed pattern wedges sothat there would be enough space between them to accommodate both thetiming eccentricity and the final servo pattern wedges that should beuniformly spaced (and thus timed). As the result, such an approach mayrequire the undesirable side effect of low sampling rate of thepatterns.

A two-step self-servowriting approach using intermediate pattern iswell-suited to solve this problem, as shown by the process in FIG. 14.Magnetic servo pattern wedges can be printed to a disk surface at step1400, which due to the mis-centering, can be non-uniformly spaced. Theprinted pattern can be read by the read element of a read/write head atstep 1402 and a corresponding intermediate servo pattern can be writtento at least one disk surface with wedges written at a pre-determinedfixed uniform spacing from the corresponding printed pattern wedges atstep 1404. Here, the intermediate pattern wedges can be “fixed” relativeto the printed pattern wedges, wherein the pre-determined fixed spacingcan be chosen to be less than the minimum spacing between any adjacentpair of printed pattern wedges so that each intermediate pattern wedgemay fall in-between a pair of printed pattern wedges. As discussedbefore, the intermediate pattern may eliminate the high noise caused bythe low frequency of the printed pattern. Since the intermediate patternwedges are distanced from the printed pattern wedges at a fixed uniformspacing, they may be also spaced between each other non-uniformly andmay suffer from the same timing eccentricity problem suffered by theprinted pattern. However, such non-uniformly spaced intermediate patternwedges may actually help to improve the sampling rate of the printedpattern since printed pattern wedges no longer need to be spaced wideapart to accommodate uniformly spaced final pattern wedges between them(at same or even higher frequencies). As discussed before, a respectiveread element of a read/write head can servo on the intermediate patternto determine the pattern runout for each track of the pattern at step1406. The intermediate pattern and the information about runout can thenbe used to write wedges final pattern at the same or higher sample rateto at least one disk surface at a uniform spacing at step 1408. The headposition can be adjusted to compensate for, and/or substantially removethe runout and wedge-write timing can be adjusted to compensate forand/or substantially remove the timing eccentricity suffered by both theprinted and intermediate patterns. Here, uniform spacing of finalpattern wedges is possible without sacrificing the sampling ratesince 1) Both intermediate pattern and final pattern are much smaller insize than the printed pattern, leaving ample space between intermediatepattern wedges to accommodate the writing of the space-efficient finalpattern wedges; 2) The final pattern wedges can be written in place ofthe printed pattern wedges if so desired, making the writing of thefinal pattern less restrictive.

Per Head and Per Cylinder Processes

In some embodiments, a disk drive such as that shown in FIG. 1 cancontain multiple disks 1000, 1004, 1006 in a disk stack as shown in FIG.10. Each surface of each disk can be capable of storing a magneticpattern 1002 written thereon by a respective write head 1010, 1012,1014, 1016, 1018, 1020. A write head, or read/write head, can be broughtinto proximity with the respective disk by an actuator arm 1008. Foractuator arms between disks, an actuator arm can have two suspensionsections each having a read head, with one suspension section for eachdisk. Two separate actuator arms also can be used, each having a readelement for the respective disk surface.

In some embodiments, a drive as shown in FIG. 10 can perform two-stepself servowriting using a per-head self-servowriting process to furtherimprove written-in runout. In such a process, intermediate servopatterns can be written via each head in the drive, and the final servopatterns can be written and/or re-written for each head independently ofeach other based on the process discussed below. Since servoing on eachhead can allow the removal of much of the spindle tilt, actuator tilteffects, and disk vibration, the per-head process allows for a removalof the non-repeatable runout for each head, which can greatly reduce theamount of written-in runout. Using such a per-head process can reducethe individual runout of head caused by disk vibrations at the possibleexpense of being a little less time-efficient.

An exemplary per-head two-step self-servowriting process is shown in theflowchart of FIG. 15. In the process, a magnetic servo pattern isprinted to a disk surface in a disk stack at step 1500, wherein theprinted media servo pattern can contain servo bursts for each concentrictrack in the pattern. The printed servo pattern can then be read using aread element on a read/write head that corresponds to the disk surfacehaving the printed pattern at step 1502. An intermediate magnetic servopattern can be written to each additional surface in the disk stack thathas a respective read/write head capable of writing information on thatsurface at step 1504. Each head can then servo on at least a portion ofthe respective intermediate pattern in order to determine runout fortracks in the pattern at step 1506. Based on the respective intermediatepattern, each head can then proceed to write and/or rewrite the finalservo pattern on its respective disk surface independently of each otherat step 1508.

In other embodiments, self-servowriting can utilize a per-cylinderinstead of a per-head approach as described below. The term cylinder isused herein as referred to the disk drive containing multiple rotatabledisks and corresponding read/write heads in a disk stack. Servoinformation read from one disk surface by one head in a cylinder can beused to write servo pattern(s) to each other disk surface in thecylinder. When a two-step printed media process is used, all heads in adrive can be used to write intermediate patterns. The drive then canselect the reference head from amongst all the heads in the drive toservo on the corresponding intermediate pattern for the writing of finalpatterns on each disk in the drive. Since the ability of a drive toservo on an intermediate pattern via a reference head can affect thequality of each final servo pattern, the drive may select a preferred or“optimal” head as the reference head, instead of selecting a referencehead without examination. In order to determine the optimal head to useas the reference head, the system can look at the non-repeatable runoutwhile servoing on each head at a couple of spots across the stroke, anddecide which head shows the lowest average amount of non-synchronousrunout, or demonstrates the best servo characteristics.

An exemplary per-cylinder two-step self-servowriting process is shown inthe flowchart of FIG. 16. Steps 1600–1606 in the process can beidentical to the steps 1500–1506 in the per-head process describedabove. At step 1608, a reference head can be selected that shows thelowest average amount of non-synchronous runout, or demonstrates thebest servo characteristics. The selected reference head can then be usedto read the respective intermediate pattern at step 1610. Suchintermediate pattern, combined with the runout information, may act as areference pattern for the writing of the final servo pattern on eachdisk surface by the respective read/write head at step 1612.

In certain situations, a per-cylinder process can be more time efficientthan the per-head process. A per-cylinder approach allows a pattern tobe replicated to each other disk in the drive one cylinder all at atime. It can also allow the final patterns in the cylinder to beexamined and re-written as necessary, or can allow the selectedreference head to be switched if another head corresponding to analternative intermediate pattern becomes preferable. In addition, aper-cylinder approach can minimize the number of movements of anactuator arms assembly when servowriting, thereby decreasing theopportunity for mechanical adjustment error and/or hysteresis.

MR Bias

Since PES noise on the printed surface can be a significant problem, itcan be desirable to use the highest safe MR bias, or the highestallowable amount of current that goes through a magneto-resistive (MR)sensor on an MR head. Increasing the MR bias can improve the ability ofa read element to properly detect and read servo information, as thesignal strength can be increased. Similar advantages can be obtainedwhen using an increased MR bias while writing servo information. Systemscan use the highest reasonable MR bias on the reference head whileservoing on the printed media surface. This can be undesirable however,as higher MR biases can have a greater probability of causing a headfailure. The failure of a head can be due to, for instance,electro-migration. Head failure can also result from high temperatures,as maintaining an MR stripe at a high temperature for a significantperiod of time can degrade performance. The tradeoff between higherprobability of head failure and higher PES noise can lead to anintermediate MR bias applied to a head. In some embodiments, a higher MRbias can be applied during the self-servowrite process since the processcan take on the order of only a few hours. Further, less time is spentwriting the intermediate wedges in a two-step process, such that it canbe acceptable to use a slightly higher MR bias during that time. Variousmethods can be used in accordance with other embodiments in order toprolong the life of an MR head, such as switching heads while the driveis idling, or turning off the MR bias between wedges when not readingdata.

Although embodiments described herein refer generally to systems havinga read/write head that can be used to write bursts on rotatable medium(magnetic media), similar advantages can be obtained with other suchdata storage systems or devices. For example, a laser writinginformation to an optical media can take advantage of additional passeswhen writing position information. Any media, or at least any rotatablemedia in a single and/or multi-headed disk drive, upon which informationis written, placed, or stored, may be able to take advantage ofembodiments of the present invention.

The foregoing description of preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many modifications andvariations will be apparent to one of ordinary skill in the relevantarts. The embodiments were chosen and described in order to best explainthe principles of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with various modifications that are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the claims and their equivalence.

1. A method for two-step self-servowriting, comprising: generating areference pattern on one surface of one or more rotatable disks in adisk stack; positioning a plurality of read/write heads relative to thesurfaces of the one or more rotatable disks; reading the referencepattern via the read/write head corresponding to the surface of the diskcontaining the reference pattern; writing an intermediate pattern oneach surface of the one or more rotatable disks; servoing on at least aportion of each of the intermediate patterns; and writing and/orrewriting a final pattern on each surface of the one or more rotatabledisks independently based on the respective intermediate pattern.
 2. Themethod according to claim 1, wherein: the reference pattern can be aprinted media pattern or a spiral pattern.
 3. The method according toclaim 1, wherein: the writing of the intermediate and final patterns canutilize a read/write head in the plurality of read/write heads, whereinthe read/write head comprises of a read element operable to read thepatterns and a write element operable to write the intermediate and/orthe final pattern.
 4. The method according to claim 1, furthercomprising: writing and/or rewriting the final pattern on each surfaceof the one or more rotatable disks individually one at a time.
 5. Themethod according to claim 1, further comprising: determining the runoutcaused by the vibration of each of the one or more rotatable disks whenservoing on the respective intermediate pattern; and reducing suchrunout when writing and/or rewriting the final pattern based on theintermediate pattern.
 6. The method according to claim 1, furthercomprising: erasing the reference pattern once each intermediate patternon each surface of the one or more rotatable disks has been written. 7.The method according to claim 1, further comprising: writing and/orrewriting a final pattern in place of the reference pattern on thecorresponding surface of the disk in the one or more rotatable disks. 8.The method according to claim 1, further comprising: erasing eachintermediate pattern once each final pattern on each surface of the oneor more rotatable disks has been written.
 9. A system for two-stepself-servowriting, comprising: one or more rotatable disks in a diskstack, wherein a surface of each of the one or more rotatable disks isoperable to contain one or more patterns including at least one of areference pattern, an intermediate pattern and a final pattern; aplurality of read/write heads, wherein each of the plurality ofread/write heads includes: a read element operable to read the one ormore patterns; and a write element operable to write the intermediateand/or the final pattern; and one or more controllers operable to:position the plurality of read/write heads relative to the surfaces ofthe one or more rotatable disks; read the reference pattern via aread/write head corresponding to the surface of the disk containing thereference pattern; write an intermediate pattern on each surface of theone or more rotatable disks via the plurality of read/write heads; andservo on at least a portion of each of the intermediate patterns; andwrite and/or rewrite a final pattern on each surface of the one or morerotatable disks independently based on the respective intermediatepattern via the plurality of read/write heads.
 10. The system accordingto claim 9, wherein; each of the one or more rotatable disks can be amagnetic disk, an optical disk, laser-recordable disk, or a rotatabledata storage device.
 11. The system according to claim 9, wherein: eachof the one or more patterns can include one or more wedges, wherein eachof the one or more wedges can include digital information and one ormore bursts.
 12. The system according to claim 9, wherein: the one ormore controllers are further operable to write and/or rewrite the finalpattern on each of the one or more rotatable disks individually one at atime.
 13. The system according to claim 9, wherein: the one or morecontrollers are further operable to: determine the runout caused by thevibration of each of the one or more rotatable disks when servoing onthe respective intermediate pattern; and reduce such runout when writingand/or rewriting the final pattern based on the intermediate pattern.14. The system according to claim 9, wherein: the one or morecontrollers are further operable to erase the reference pattern onceeach intermediate pattern on each surface of the one or more rotatabledisks has been written.
 15. The system according to claim 9, wherein:the one or more controllers are further operable to write and/or rewritea final pattern in place of the reference pattern on the correspondingsurface of the disk in the one or more rotatable disks.
 16. The systemaccording to claim 9, wherein: the one or more controllers are furtheroperable to erase each intermediate pattern once each final pattern oneach surface of the one or more rotatable disks has been written.
 17. Asystem for two-step self-servowriting, comprising: means for generatinga reference pattern on one surface of a one or more rotatable disks in adisk stack; means for positioning a plurality of read/write headsrelative to the surfaces of the one or more rotatable disks; means forreading the reference pattern via the read/write head corresponding tothe surface of the disk containing the reference pattern; means forwriting an intermediate pattern on each surface of the one or morerotatable disks; means for servoing on at least a portion of each of theintermediate patterns; and means for writing and/or rewriting a finalpattern on each surface of the one or more rotatable disks independentlybased on the respective intermediate pattern.